Highly porous graphenated graphite felt electrodes with catalytic defects for high-performance vanadium redox flow batteries produced via NiO/Ni redox reactions

Because of their outstanding features such as safety, long cycle life, and design flexibility, vanadium redox flow batteries (VRFBs) have attracted much attention from those involved in the development of electrical energy-storage system. However, the performance of VRFBs remains limited due to their significant polarization. Here, we report a new fabrication method for highly porous graphenated graphite felt electrode with high-performance, which enables operation of VRFBs at high current rates by alleviating polarization. The etched graphite felt (EGF) electrode is optimized by repetition of a NiO/Ni redox reaction cycle, which is a facile, scalable, and controllable etching process that produces a high surface area. The EGF also has stepped edges, which act as preferred sites for incorporating oxygen defects. The plentiful oxygen defects on the stepped edges show catalytic effect and good wettability for vanadium electrolyte, leading to substantially reduced overpotentials. VRFBs with the EGF electrode exhibit a strongly enhanced electrochemical performance with respect to energy efficiency and discharge capacity at 150 mA cm−2. Furthermore, the robustness of the graphenated structure provides stability and durability in acidic electrolyte during long-term battery operation, facilitating stable cycling performance for 200 cycles at high current rates.